A group of male, Sprague Dawley rats will be studied with respect to two effects. First, the absorption and retention of chromium (III) complexes of macrocyclic compounds and other ligands by the rat using Cr51 tracers. No ligand studied by us has yet proved effective in increasing Cr absorption or retention by the rat. Second, a group of weanling rats will be made chromium-deficient and their glucose tolerance measured. We have placed a group of normal, young rats on a chromium-deficient diet, and have found that one-third of these rats show abnormally low glucose tolerance (i.e. removal rates below 2.5 percent/min.). Human autopsy samples (liver, spleen, aorta, kidney, abdominal fat tissue and hair) from the Phoenix Indian hospital and the St. Louis Veterans Hospital will be analyzed for chromium. Samples from Phoenix will be from members of the Pima Indian tribe, with and without diagnosed diabetes, while those from St. Louis will be from atherosclerotic patients. All samples received from Phoenix will be well documented by members of the NIH-supported group there with respect to dietary and medical histories. All chromium analyses will be done using a Perkin Elmer Model 305A equipped with a graphite furnace allowing measurement of chromium at the part per billion level. A series of square planar chromium (III) complexes has been synthesized in which rapid replacement reactions are found for the axial ligands. These include tetraphenylporphyrin type ligands. Determinations will be made of the log K, delta H super o and delta S super o values associated with the reaction of these complexes with ligands containing various donor atoms (i.e. COO minus, NH2, S equals, imidazole N) and with insulin in order to characterize chromium (III) reactions.